1. Field of the Invention
The present invention relates generally to an automatic power interrupting apparatus, and more particularly to an automatic photosensitive switching circuit for use in an electric appliance. Further, the present invention also relates to a temperature control circuit for use in an electric appliance employing a heat driven element.
2. Description of the Related Art
Conventional electric pressing irons have been used for many years to press clothing and various textiles. Such conventional irons operate in that a sole plate component is heated to a sufficient temperature suitable to press and/or remove wrinkles from clothing or various textiles. It is well known in the prior art for pressing irons, and in particular the soleplate element, to be selectively controlled to operate at various temperature levels enabling different types of fabrics to be effectively ironed without causing damage. It is also well known that the efficiency of the iron directly correlates with the temperature of the sole plate element, such that it is desirable to iron a particular fabric at the highest temperature to which it can be subjected for a reasonable period of time without scorching. The conventional iron typically utilizes a bimetallic thermostatic control to regulate the temperature of the soleplate so as to be within the temperature operating range of a desired setting.
However, an inherent safety problem exists with the conventional household iron, in that the iron is prone to scorch clothing, cause fires or cause burns to a person who inadvertently contacts the heated soleplate of the iron. For example, an article of clothing can be scorched by the iron, when the heated soleplate of the iron is left in a horizontal position and remains in direct contact with the clothing for a prolonged period of time. Such an event commonly occurs when the attention of the user is directed away from the iron. Further, and more seriously, the aforementioned event may lead to effect the article of clothing to ignite in flames, potentially creating a fire in the household. Moreover, a person, commonly a child, may contact the energized heated soleplate of an unattended iron which is left to remain in an upstanding position, typically causing severe burns to such a person. Thus, a need has existed to provide an automatic power interrupting circuit in a conventional household iron to de-energize the heating element in the soleplate of the iron, when the iron is left unattended for a prolonged period of time.
An attempt to address the above-mentioned need was to provide a position/motion sensitive electrochemical switch, such as a mercury switch in the circuitry of the iron. Essentially, the mercury switch is operational to de-energize the heated element in the soleplate in the event the iron is left unattended for a prolonged period of time. Examples of such mercury switches can be found, in Townsend, U.S. Pat. No. 4,203,101; Nawrot et al., U.S. Pat. No. 4,686,352; Borsari et al., U.S. Pat. No. 4,692,589 and Albinger, Jr., U.S. Pat. No. 4,745,260. Briefly, an iron utilizing the aforementioned mercury switch functions such that when the iron is in a horizontal position and in motion, the mercury switch is closed to energize the heating element. However, if the iron is to remain motionless in such a horizontal position for a predetermined period of time, such as thirty (30) seconds, the control circuitry of the iron is configured to de-energize the soleplate until movement of the iron resumes. Further, if the iron is positioned in a vertical position, or at an angled position relative to the horizontal resting plane of the iron, the mercury switch is opened and the circuitry of the iron is configured to de-energize the heating element in the sole-plate after a second predetermined period of time has elapsed when the iron remains in such a vertically oriented position.
Two apparent disadvantages are associated with the employment of the aforementioned mercury switch in an iron. First, during the initial start-up period in which the heating element is first energized, the heating element typically requires a prolonged period of time, such as two and a half (2.5) minutes to reach a selected optimum temperature for ironing. However, the aforementioned prior art iron employing a mercury switch may only initially heat-up when the iron is positioned in a vertical orientation, since when the iron is positioned motionless in a horizontal orientation, the heating element will de-energize after a short period of time, such as thirty (30) seconds. Thus, the prior art iron may only initially heat-up when it is positioned in a vertical orientation whereby the heating element must remain energized while the iron is vertically oriented for a period of time (i.e., two and half (2.5) minutes) which is sufficient to enable the soleplate to reach a selected optimum temperature. This is disadvantageous in that every time the iron is positioned in a vertical orientation, the heating element must remain energized for a prolonged period of time (i.e., two and half (2.5 ) minutes) before the heating element is automatically de-energized. This prolonged period of time may potentially create a dangerous situation since the energized soleplate is exposed while vertically oriented which may cause severe bums to a person who inadvertently contacts the exposed upstanding soleplate while the heating element is being energized. Further, the later time period may create a fire hazard whereby the unattended energized iron may be caused to fall from the ironing table when in a relatively unstable vertical position, and consequently come into contact with ignitable material.
Moreover, it has been found that many users prefer to allow the soleplate to initially heat up when the iron is positioned in a horizontal position, preferably in a fireproof tray suitable for such a purpose. It is noted that an advantage exists in permitting the iron to initially heat up while in a horizontal position, in that the iron is more stable in such a position in contrast to the less stable vertical position. It is thus readily apparent that an iron employing the aforementioned mercury switch is unable to permit the iron to initially heat up while disposed in a horizontal position, since energization of the heating element is only typically limited to twenty (20) seconds when an iron is to remain motionless in a horizontal orientation.
Secondly, an iron employing an aforementioned mercury switch is disadvantageous in that the reliability of its power switching circuit depends upon the functionability of the mercury switch. For example, when in a horizontal position, and when the user is operating the iron in smooth movements without great acceleration or deceleration for a prolonged period of time, the mercury switch may not change its state (from an open to a closed state and vice versa) causing the control circuit to incorrectly determine the iron is in a period of non-use resulting in the de-energization of the heated element. Furthermore, it is disadvantageous to employ the premise of movement to determine the energization of the heating element, as an unattended iron may be inadvertently moved, or may accidentally fall from the ironing board effecting the control circuit of the unattended iron to re-energize the heating element which may bring about a safety and fire hazard.
Another disadvantage which exists with the conventional iron is that the aforementioned bimetallic thermostat is prone to numerous setbacks. One such setback is that the effectiveness of the bimetallic thermostat to regulate temperature will decrease with time due to inherent metal fatigue within the bimetallic switching element. Further, the user often has to set the bimetallic thermostatic control at a considerably reduced temperature from the maximum at which the iron can be safely operated due to the well known fact that the soleplate temperature has a tendency to oscillate between a relatively low temperature when the soleplate is initially energized and at a relatively high temperature when the soleplate is initially de-energized. Such oscillations adversely effect the temperature regulation of the soleplate of the iron.
Accordingly, it is the primary object of the present invention to overcome the above-mentioned setbacks of a conventional iron utilizing the aforementioned mercury switch and/or bimetallic thermostatic control.